Analysis of Caesarean-Section rates according to Robson's ten group classification system and evaluating the indications within the groups

Background: With Caesarean sections on the rise WHO proposes that health care facilities use the Robson's 10 group classification system to audit their C-sections rates. This classification would help understand the internal structure of the CS rates at individual health facilities identify key population groups, indications in each group and formulate strategies to reduce these rates.Methods: This was a cross sectional study for a period of 24 months at a tertiary care hospital in a tribal area of Kerala South India. Women who delivered during this period were included and classified into 10 Robson's classes and percentages were calculated for the overall rate, the representation of groups, contribution of groups and Caesarean percentage in each group.Results: Highest contribution was by Group 5 and Group 2. Together these two groups contributed to 38% of the total Caesareans. Followed by Group 8 and 10. All four added contributed to 63% of the section rate The least contribution was by Group 3. Groups 6, 7 and 9 by themselves did not contribute much but within their groups had a 100% C-Section rate.Conclusions: The contribution of the various Robson's Group to the absolute C-Section rates needs to be looked into. Reducing primary section rates, adequate counselling and encouraging for VBAC, changing the norms for dystocia and non-reassuring fetal status, training and encouraging obstetricians to perform versions when not contraindicated could reduce the contribution of Robson's groups towards the absolute C-Section rates

Optimized reflector stacks for solidly mounted bulk acoustic wave resonators

The quality factor (Q) of a solidly mounted bulk acoustic wave resonator (SMR) is limited by substrate losses, because the acoustic mirror is traditionally optimized to reflect longitudinal waves only. We propose two different design approaches derived from optics to tailor the acoustic mirror for effective reflection of both longitudinal and shear waves. The first one employs the stopband theory in optics; the second one takes advantage of the periodic nature of reflection spectra in a Bragg reflector: the diffraction grating design approach. The optimized design using stopband theory reaches a calculated minimum transmission of −25 dB and −20 dB at resonance frequency for longitudinal and shear waves, respectively, for various practical reflector material combinations. Using the diffraction grating approach, a near quarter-wave performance is maintained for longitudinal waves, whereas shear waves reach minimum transmission below −26 dB. However, this design does necessitate relatively thick layers. The experimental results show good agreement with finite element models (FEM).\ud The extracted 1-D Q for the realized shear optimized devices was increased to around 3300.\u

Reflector stack optimization for Bulk Acoustic Wave resonators

Thin-film bulk-acoustic-wave (BAW) devices are used for RF selectivity in mobile communication system and other wireless applications. Currently, the conventional RF filters are getting replaced by BAW filters in all major cell phone standards. In this thesis, we study solidly mounted BAW resonators (SMR) which are building blocks of these filters. The good selectivity offered by the BAW resonators makes them excellent components for inter-stage filters and duplexers for mobile applications

Opportunities for shear energy scaling in bulk acoustic wave resonators

An important energy loss contribution in bulk acoustic wave resonators is formed by so-called shear waves, which are transversal waves that propagate vertically through the devices with a horizontal motion. In this work, we report for the first time scaling of the shear-confined spots, i.e., spots containing a high concentration of shear wave displacement, controlled by the frame region width at the edge of the resonator. We also demonstrate a novel methodology to arrive at an optimum frame region width for spurious mode suppression and shear wave confinement. This methodology makes use of dispersion curves obtained from finite-element method (FEM) eigenfrequency simulations for arriving at an optimum frame region width. The frame region optimization is demonstrated for solidly mounted resonators employing several shear wave optimized reflector stacks. Finally, the FEM simulation results are compared with measurements for resonators with Ta2O5/SiO2 stacks showing suppression of the spurious modes

Solidly Mounted Resonator with Optimized Acoustic Reflector

The quality factor (Q) of the Solidly Mounted Resonator is limited by acoustic losses caused by waves leaking through the mirror stack. Traditionally employed acoustic mirror reflects only longitudinal waves and not shear waves. Starting with the stop-band theory and the principle of spacer layers in Optics, we present a design procedure which gives the modified thicknesses for the reflector stack to efficiently reflect both the waves. FEM simulations were performed for verifying the results based on the analytical model described in showing good agreement. With the optimized design, we can obtain a minimum transmission for longitudinal and shear waves of -25 dB and -20 dB at resonant frequencies for longitudinal and shear waves, respectively, for various reflector material combinations. With such optimized designs, devices can be designed that are no more limited by acoustic loss into the substrate